From "hidden" to "onion" is just a terminology change. For the v2/v3 change, not sure there is an in-depth blog post on the differences except for comparing the specs of v2[0] vs v3[1]. There's a wiki page with a high-level overview [2].

0 - https://github.com/torproject/torspec/blob/master/rend-spec-... 1 - https://github.com/torproject/torspec/blob/master/rend-spec-... 2 - https://trac.torproject.org/projects/tor/wiki/doc/NextGenOni...